ADD WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track D. Wing
Expires: August 24, 2021 Citrix
M. Richardson
Sandelman Software Works
M. Boucadair
Orange
February 20, 2021
DNS Server Selection: DNS Server Information with Assertion Token
draft-reddy-add-server-policy-selection-06
Abstract
The document defines a mechanism that is meant to communicate DNS
resolver information to DNS clients for use as a criteria for server
selection decisions. In particular, the document defines a mechanism
for a DNS server to communicate its filtering behavior to DNS
clients. Such an information that is cryptographically signed to
attest its authenticity is used for the selection of DNS resolvers.
Typically, evaluating the filtering behavior and the signatory, DNS
clients with minimal or no human intervention can select the DNS
servers for resolving domain names.
This assertion is useful for encrypted DNS (e.g., DNS-over-TLS, DNS-
over-HTTPS, or DNS-over-QUIC) servers that are either public
resolvers or discovered in a local network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 24, 2021.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Policy Assertion Token (PAT): Overview . . . . . . . . . . . 4
4. PAT Header . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. 'typ' (Type) Header Parameter . . . . . . . . . . . . . . 6
4.2. 'alg' (Algorithm) Header Parameter . . . . . . . . . . . 6
4.3. 'x5u' (X.509 URL) Header Parameter . . . . . . . . . . . 7
4.4. An Example of PAT Header . . . . . . . . . . . . . . . . 7
5. PAT Payload . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. JWT Defined Claims . . . . . . . . . . . . . . . . . . . 8
5.1.1. 'iat' - Issued At Claim . . . . . . . . . . . . . . . 8
5.1.2. 'exp' - Expiration Time Claim . . . . . . . . . . . . 8
5.2. PAT Specific Claims . . . . . . . . . . . . . . . . . . . 8
5.2.1. DNS Server Identity Claims . . . . . . . . . . . . . 8
5.2.2. 'policyinfo' (Policy Information) Claim . . . . . . . 9
5.2.3. An Example . . . . . . . . . . . . . . . . . . . . . 10
6. PAT Signature . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Extending PAT . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Deterministic JSON Serialization . . . . . . . . . . . . . . 12
8.1. Example PAT Deterministic JSON Form . . . . . . . . . . . 13
9. Using SVCB Responses . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
11.1. Media Type Registration . . . . . . . . . . . . . . . . 15
11.1.1. Media Type Registry Contents Additions Requested . . 15
11.2. JSON Web Token Claims Registration . . . . . . . . . . . 16
11.2.1. Registry Contents Additions Requested . . . . . . . 16
11.3. DNS Resolver Information Registration . . . . . . . . . 16
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
13.1. Normative References . . . . . . . . . . . . . . . . . . 17
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13.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Example of ES256-based PAT JWS Serialization and
Signature . . . . . . . . . . . . . . . . . . . . . 20
A.1. X.509 Private Key in PKCS#8 Format for ES256 Example** . 22
A.2. X.509 Public Key for ES256 Example** . . . . . . . . . . 22
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures . . . . . . . . . . . . . . . . 22
B.1. X.509 Private Key in PKCS#8 format for E384 Example** . . 23
B.2. X.509 Public Key for ES384 Example** . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
[RFC7626] discusses DNS privacy considerations in both "on the wire"
(Section 2.4 of [RFC7626]) and "in the server" (Section 2.5 of
[RFC7626]) contexts. Examples of protocols that provide encrypted
channels between DNS clients and servers are DNS-over-HTTPS (DoH)
[RFC8484], DNS-over-TLS (DoT) [RFC7858], and DNS-over-QUIC (DoQ)
[I-D.ietf-dprive-dnsoquic].
DNS clients can discover and authenticate encrypted DNS servers
provided by a local network, for example using the techniques
proposed in [I-D.btw-add-home] and [I-D.ietf-add-ddr]. If the
mechanism used to discover the encrypted DNS server is insecure, the
DNS client needs evidence about the encrypted server to assess its
trustworthiness and a way to appraise such evidence. The mechanism
specified in this document can be used by the DNS client to
cryptographically identify if it is connecting to an encrypted DNS
server hosted by a specific organization (e.g., ISP or Enterprise).
This strengthens the protection as clients can detect and reject
connections to encrypted DNS servers hosted by attackers.
This document also defines a mechanism for DNS clients to gather a
set of information related to discovered (or preconfigured) servers
and use that information to feed a DNS server selection procedure.
The following parameters are supported in this version:
Malware blocking: Indicates whether the DNS server offers malware
blocking service.
Phishing blocking: Indicates whether the DNS server offers phishing
blocking service.
Policy blocking: Indicates whether the DNS server maintains a block-
list due to a policy by the operator of the DNS server.
Censored blocking: Indicates whether the DNS server maintains a
block-list based on a requirement from an external entity.
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Filtered blocking: Indicates whether the DNS server maintains a
block-list based on the request from the client .
QNAME minimization: Indicates whether the DNS server supports QNAME
minimisation [RFC7816].
Extended error: Indicates whether the DNS server supports extended
DNS error (EDE) [RFC8914].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document makes use of the terms defined in [RFC8499] and
[I-D.ietf-dnsop-terminology-ter].
'Encrypted DNS' refers to a DNS protocol that provides an encrypted
channel between a DNS client and server (e.g., DoT, DoH, or DoQ).
The terms 'Evidence', 'Verifier', 'Background Check', 'Relying
Party', 'Appraisal Policy', and 'Attestation Results' are defined in
[I-D.ietf-rats-architecture].
3. Policy Assertion Token (PAT): Overview
The mechanism used in this specification resembles the Background-
Check Model discussed in Sections 5.2 and 5.3 of Remote attestation
procedure (RATS) Architecture [I-D.ietf-rats-architecture]. RATS
enables a relying party to establish a level of confidence in the
trustworthiness of a remote peer through the creation of Evidence to
assess the peer's trustworthiness, and an Appraisal Policy for such
Evidence.
In this document, the Relying Party is the DNS client and the
Attester is the encrypted DNS server. The Encrypted DNS servers MAY
use "Domain Validation" (DV) certificates for certificate-based
server authentication in TLS connections.
The DNS server's resolver information needs to be validated and
signed. This signature is called an Attestation Result
[I-D.ietf-rats-architecture]. This validation can be performed by
the DNS operator itself (signed by the DNS operator's certificate)
acting as a verifier or performed by an external Verifier (signed by
that external Verifier). The signing certificate can to be an
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Extended Validation (EV) certificate issued by a public CA in
specific scenarios listed below. An EV certificate is issued by the
public CA after a thorough Background Check to verify the requesting
organization's legal identity. If the signing certificate is a EV
certificate, it leaves the client with a better audit trail of the
organization hosting the DNS server in comparison with the DV
certificate.
The use of EV certificate is needed in the following scenarios:
o It helps the client to avoid sending DNS queries to an Encrypted
DNS server hosted by an attacker discovered insecurely (e.g.,
using DHCP/RA or DNS). For example, an attacker can get a domain
name, domain-validated public certificate from a CA and host a
Encrypted DNS server. Furthermore, an attacker can use a public
IP address, get an 'IP address'-validated public certificate from
a CA and host a Encrypted DNS server.
o It can be used by the client to identify the Encrypted DNS server
is hosted by a legal organization.
The use of EV certificate is not required in the following scenarios:
o If the Encrypted DNS server can only be discovered securely (e.g.,
using IKEv2 [I-D.btw-add-ipsecme-ike]), the signing certificate
need not be an EV certificate.
o Secure Zero Touch Provisioning [RFC8572] defines a bootstrapping
strategy for enabling a networking device to securely obtain the
required configuration information with no user input. If the
encrypted DNS server is insecurely discovered and not
preconfigured in the networking device, the DNS client on the
networking device can validate the Policy Assertion Token
signature using the owner certificate as per Section 3.2 of
[RFC8572].
JSON Web Token (JWT) [RFC7519] and JSON Web Signature (JWS) [RFC7515]
and related specifications define a standard token format that can be
used as a way of encapsulating claimed or asserted information with
an associated digital signature using X.509 based certificates. JWT
provides a set of claims in JSON format that can accommodate asserted
policy information of the Encrypted DNS server. Additionally, JWS
provides a path for updating methods and cryptographic algorithms
used for the associated digital signatures.
JWS defines the use of JSON data structures in a specified canonical
format for signing data corresponding to JOSE header, JWS Payload,
and JWS Signature. The next sections define the header and claims
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that MUST be minimally used with JWT and JWS for policy assertion
token.
The Policy Assertion Token (PAT) specifically uses this token format
and defines claims that convey the policy information of Encrypted
DNS server.
The client can retrieve the PAT object using the SVCB RRtype defined
in [I-D.ietf-dnsop-svcb-https] and QNAME of the domain name that is
used to authenticate the DNS server (referred to as ADN in
[RFC8310]). If the special use domain name "resolver.arpa" defined
in [I-D.ietf-add-ddr] is used to discover the Encrypted DNS server,
the client can retrieve the PAT object using the SVCB RRtype and
QNAME of the special use domain name.
The signature of PAT object MUST be validated by the DNS client. If
signature is invalid, the PAT object is rejected. If signature is
valid, signer is trusted and the contents of the PAT object comply
with the user's requirements, the DNS client can use that encrypted
DNS server. The result of this determination SHOULD be remembered by
the DNS client to avoid prompting the user again when re-joining that
same network.
4. PAT Header
The JWS token header is a JOSE header (Section 4 of [RFC7515]) that
defines the type and encryption algorithm used in the token.
The PAT header MUST include, at a minimum, the header parameters
defined in Sections 4.1, 4.2, and 4.3.
4.1. 'typ' (Type) Header Parameter
The 'typ' (Type) Header Parameter is defined in Section 4.1.9 of
[RFC7515] to declare the media type of the complete JWS.
For PAT Token the 'typ' header MUST be the string 'pat'. This
represents that the encoded token is a JWT of type pat.
4.2. 'alg' (Algorithm) Header Parameter
The 'alg' (Algorithm) Header Parameter is defined in Section 4.1.1 of
[RFC7515]. It specifies the JWS signature cryptographic algorithm.
It also refers to a list of defined 'alg' values as part of a
registry established by JSON Web Algorithms (JWA) [RFC7518]
Section 3.1.
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For the creation and verification of PAT tokens and their digital
signatures, implementations MUST support ES256 as defined in
Section 3.4 of [RFC7518]. Implementations MAY support other
algorithms registered in the JSON Web Signature and Encryption
Algorithms registry created by [RFC7518]. The content of that
registry may be updated in the future depending on cryptographic
strength requirements guided by current security best practice. The
mandatory-to-support algorithm for PAT tokens may likewise be updated
in the future.
Implementations of PAT digital signatures using ES256 as defined
above SHOULD use deterministic ECDSA when supported for the reasons
stated in [RFC6979].
4.3. 'x5u' (X.509 URL) Header Parameter
As defined in Section 4.1.5 of [RFC7515], the 'x5u' header parameter
defines a URI [RFC3986] referring to the resource for the X.509
public key certificate or certificate chain [RFC5280] corresponding
to the key used to digitally sign the JWS. Generally, as defined in
Section 4.1.5 of [RFC7515] this corresponds to an HTTPS or DNSSEC
resource using integrity protection.
4.4. An Example of PAT Header
An example of the PAT header is shown in Figure 1. It includes the
specified PAT type, ES256 algorithm, and an URI referencing the
network location of the certificate needed to validate the PAT
signature.
{
"typ":"pat",
"alg":"ES256",
"x5u":"https://cert.example.com/pat.cer"
}
Figure 1: A PAT Header Example
5. PAT Payload
The token claims consist of the policy information of the DNS server
that needs to be verified at the DNS client. These claims follow the
definition of a JWT claim (Section 4 of [RFC7519]) and are encoded as
defined by the JWS Payload (Section 3 of [RFC7515]).
PAT defines the use of a standard JWT-defined claim as well as custom
claims corresponding to the DoT or DoH servers.
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Claim names MUST use the US-ASCII character set. Claim values MAY
contain characters that are outside the ASCII range, however they
MUST follow the default JSON serialization defined in Section 7 of
[RFC7519].
5.1. JWT Defined Claims
5.1.1. 'iat' - Issued At Claim
The JSON claim MUST include the 'iat' (Section 4.1.6 of [RFC7519])
defined claim "Issued At". The 'iat' should be set to the date and
time of issuance of the JWT. The time value should be of the format
(NumericDate) defined in Section 2 of [RFC7519].
5.1.2. 'exp' - Expiration Time Claim
The JSON claim MUST include the 'exp' (Section 4.1.4 of [RFC7519])
defined "claim Expiration Time". The 'exp' should be set to specify
the expiration time on or after which the JWT is not accepted for
processing. The PAT object should expire after a reasonable
duration. A short expiration time for the PAT object periodically
reaffirms the policy information of the DNS server to the DNS client
and ensures the DNS client does not use outdated policy information.
If the DNS client knows the PAT object has expired, it should make
another request to get the new PAT object from the DNS server.
5.2. PAT Specific Claims
5.2.1. DNS Server Identity Claims
The DNS server identity is represented by a claim that is required
for PAT: the 'server' claim. The 'server' MUST contain claim values
that are identity claim JSON objects where the child claim name
represents an identity type and the claim value is the identity
string, both defined in subsequent subsections.
These identities can be represented as either authentication domain
name (ADN) (defined in [RFC8310]) or Uniform Resource Indicators
(URI).
The DNS client constructs a reference identifier for the DNS server
based on the ADN or the domain portion in the URI of the DNS server
identity. The domain name in the DNS-ID identifier type within
subjectAltName entry in the DNS server certificate conveyed in the
TLS handshake is matched with the reference identifier. If the match
is not successful, the client MUST not accept the PAT for further
processing.
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5.2.1.1. 'adn' - Authentication Domain Name Identity
If the DNS server identity is an ADN, the claim name representing the
identity MUST be 'adn'. The claim value for the 'adn' claim is the
ADN.
5.2.1.2. 'uri' - URI Identity
If the DNS server identity is of the form URI Template, as defined in
[RFC6570], the claim name representing the identity MUST be 'uri' and
the claim value is the URI Template form of the DNS server identity.
As a reminder, if DoH is supported by the DNS server, the DNS client
uses the URI Template (Section 3 of [RFC8484]).
5.2.2. 'policyinfo' (Policy Information) Claim
The 'policyinfo' claim MUST be formatted as a JSON object. The JSON
object MUST use the I-JSON message format defined in [RFC7493]. Note
that [RFC7493] was based on [RFC7159], but [RFC7159] was replaced by
[RFC8259]. Requiring the use of I-JSON instead of more general JSON
format greatly increases the likelihood of interoperability.
The 'policyinfo' claim contains the policy information of the DNS
server, it includes the following attributes:
filtering: If the DNS server changes some of the answers that it
returns or failure codes are returned based on policy criteria,
such as to prevent access to malware sites or objectionable
content (e.g., legal obligation). This optional attribute has the
following structure:
malwareblocking: The DNS server offers malware blocking service.
If access to domains is blocked on threat data, the parameter
value is set to 'true'. Note that some of the commonly known
types of malware are viruses, worms, trojans, bots, ransomware,
backdoors, spyware, and adware.
phishingblocking: The DNS server offers phishing blocking
service. If access to phishing domains is blocked, the
parameter value is set to 'true'.
policyblocking: If access to domains is blocked due to an
internal policy imposed by the operator of the DNS server, the
parameter value is set to 'true'. Note that the extended error
code "Blocked" defined in Section 4.16 of [RFC8914] identifies
access to domains is blocked due to an policy by the operator
of the DNS server.
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censoredblocking: If access to domains is blocked due to an
external requirement imposed by an external entity, the
parameter value is set to 'true'. Note that the extended error
code "Censored" defined in Section 4.17 of [RFC8914] identifies
access to domains is blocked based on a requirement from an
external entity. Similar to the definition of "Censored"
blocking in [RFC8914], this version of the specification does
not distinguish blocking from regulatory bodies (e.g., Law
Enforcement Agency) vs. arbitrary blocking. Such
differentiation may be defined if required.
filteredblocking: If access to domains is blocked due to an
blacklist requested by the client, the parameter value is set
to 'true'. Note that the extended error code "Filtered"
defined in Section 4.18 of [RFC8914] identifies access to
domains is blocked based on the request from the client to
blacklist domains.
qnameminimization: If the DNS server supports QNAME minimisation
[RFC7816] to improve DNS privacy, the parameter value is set to
true. This is a mandatory attribute.
extendeddnserror: If the DNS server supports extended DNS error
(EDE) [RFC8914] to return additional information about the cause
of DNS errors, the parameter value is set to true. This is an
optional attribute.
clientauth: If the DNS server policy requires client authentication,
the parameter value is set to true. For example, when not on the
enterprise network (e.g., at home or coffee shop) yet needing to
access the enterprise Encrypted DNS server, roaming users can use
client authentication to access the Enterprise provided Encrypted
DNS server. This is an optional attribute.
resinfourl: A URL that points to the generic unstructured resolver
information (e.g., DoH APIs supported, possible HTTP status codes
returned by the DoH server, how to report a problem, etc.) for
troubleshooting purpose. This is an optional attribute.
5.2.3. An Example
Figure 2 shows an example of policy information.
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{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"filtering": {
"malwareblocking": true,
"policyblocking": false
},
"qnameminimization":false,
}
}
Figure 2: An Example of Policy Information
6. PAT Signature
The signature of the PAT is created as specified in Section 5.1 of
[RFC7515] (Steps 1 through 6). PAT MUST use the JWS Protected
Header.
For the JWS Payload and the JWS Protected Header, the lexicographic
ordering and white space rules described in Section 4 and Section 5,
and JSON serialization rules in Section 8 MUST be followed.
The PAT is cryptographically signed by the domain hosting the DNS
server and optionally by a third party who performed privacy and
security audit of the DNS server.
The policy information is attested using "Extended Validation" (EV)
certificate to avoid bad actors taking advantage of this mechanism to
advertise encrypted DNS servers for illegitimate and fraudulent
purposes meant to trick DNS clients into believing that they are
using a legitimate encrypted DNS server hosted to provide privacy for
DNS transactions.
Alternatively, a DNS client has to be configured to trust the leaf of
the signer of the PAT object. That is, trust of the signer MUST NOT
be determined by validating the signer via the OS or the browser
trust chain because that would allow any arbitrary entity to operate
a DNS server and assert any sort of policy.
Appendix A provides an example of how to follow the steps to create
the JWS Signature.
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JWS JSON serialization (Step 7 in Section 5.1 of [RFC7515]) is
supported for PAT to enable multiple signatures to be applied to the
PAT object. For example, the PAT object can be cryptographically
signed by the domain hosting the DNS server and by a third party who
performed privacy and security audit of the DNS server.
Appendix B includes an example of the full JWS JSON serialization
representation with multiple signatures.
Section 5.1 of [RFC7515] (Step 8) describes the method to create the
final JWS Compact Serialization form of the PAT Token.
7. Extending PAT
PAT includes the minimum set of claims needed to securely assert the
policy information of the DNS server. JWT supports a mechanism to
add additional asserted or signed information by simply adding new
claims. PAT can be extended beyond the defined base set of claims to
represent other DNS server information requiring assertion or
validation. Specifying new claims follows the baseline JWT
procedures (Section 10.1 of [RFC7519]). Understanding new claims on
the DNS client is optional. The creator of a PAT object cannot
assume that the DNS client will understand the new claims.
8. Deterministic JSON Serialization
JSON objects can include spaces and line breaks, and key value pairs
can occur in any order. It is therefore a non-deterministic string
format. In order to make the digital signature verification work
deterministically, the JSON representation of the JWS Protected
Header object and JWS Payload object MUST be computed as follows.
The JSON object MUST follow the following rules. These rules are
based on the thumbprint of a JSON Web Key (JWK) as defined in
Section 3 of [RFC7638] (Step 1).
1. The JSON object MUST contain no whitespace or line breaks before
or after any syntactic elements.
2. JSON objects MUST have the keys ordered lexicographically by the
Unicode [UNICODE] code points of the member names.
3. JSON value literals MUST be lowercase.
4. JSON numbers are to be encoded as integers unless the field is
defined to be encoded otherwise.
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5. Encoding rules MUST be applied recursively to member values and
array values.
8.1. Example PAT Deterministic JSON Form
This section demonstrates the deterministic JSON serialization for
the example PAT Payload shown in Section 5.2.3.
The initial JSON object is shown in Figure 3.
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"qnameminimization":false,
}
}
Figure 3: Initial JSON Object
The parent members of the JSON object are as follows, in
lexicographic order: "exp", "iat", "policyinfo", "server".
The final constructed deterministic JSON serialization
representation, with whitespace and line breaks removed, (with line
breaks used for display purposes only) is:
{"exp":1443640345,"iat":1443208345,
"policyinfo":{"qnameminimization":false},
"server":{"adn":["example.com"]}}
Figure 4: Deterministic JSON Form
9. Using SVCB Responses
This document defines the following entries for the IANA SVCB Service
Parameters registry that is defined in [I-D.ietf-dnsop-svcb-https].
1. The "server" name containing the DNS server identity discussed in
Section 3.
2. The sub-attribute "adn" discussed in Section 3 contained in the
"server" attribute is used to specify the DNS server identity in
the form of ADN.
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3. The sub-attribute "uri" discussed in Section 3 contained in the
"server" attribute is used to specify the DNS server identity in
the form of URI template.
4. The "filtering", "resinfourl", "extendeddnserror" and
"qnameminimization" names containing the resolver information of
the DNS server discussed in Section 3.
5. The sub-attributes "malwareblocking", "phishingblocking",
"policyblocking", "filteredblocking", and "censoredblocking"
discussed in Section 3 contained in the "filtering" attribute are
used to specify the reasons for performing DNS-based content
filtering.
6. The "attested-resinfo" name contains a base64 encoding of a PAT
Section 3. If the "attested-resinfo" name is conveyed to the
client, the server need not convey the above attributes (1 to 5)
separately as that resolver information will be extracted by the
client from the PAT payload.
10. Security Considerations
The use of PAT object based on the validation of the digital
signature and the associated certificate requires consideration of
the authentication and authority or reputation of the signer to
attest the policy information of the DNS server being asserted. Bad
actors can host encrypted DNS servers to invade the privacy of the
user. Bad actor can get a domain name, host encrypted DNS servers,
and get the DNS server certificate signed by a CA. The policy
information will have to be attested using EV certificates or a PAT
object signer trusted by the DNS client to prevent the attack.
The CA that issued the EV certificate does not attest the resolver
information. The organization hosting the DNS server attests the
resolver information using the EV certificate and the client uses the
EV certificate to identify the organization (e.g., ISP or Enterprise)
hosting the DNS server.
If the PAT object is asserted by a third party, it can do a "time of
check" but the DNS server is susceptible of "time of use" attack.
For example, changes to the policy of the DNS server can cause a
disagreement between the auditor and the DNS server operation, hence
the PAT object needs to be also asserted by the domain hosting the
DNS server. In addition, the PAT object needs to have a short
expiration time (e.g., 7 days) to ensure the DNS server's domain re-
asserts the policy information and limits the damage from change in
policy and mis-issuance.
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11. IANA Considerations
11.1. Media Type Registration
11.1.1. Media Type Registry Contents Additions Requested
This section registers the 'application/pat' media type [RFC2046] in
the 'Media Types' registry in the manner described in [RFC6838],
which can be used to indicate that the content is a PAT defined JWT.
o Type name: application
o Subtype name: pat
o Required parameters: n/a
o Optional parameters: n/a
o Encoding considerations: 8bit; application/pat values are encoded
as a series of base64url-encoded values (some of which may be the
empty string) separated by period ('.') characters..
o Security considerations: See the Security Considerations
Section of [RFC7515].
o Interoperability considerations: n/a
o Published specification: [THIS_DOCUMENT]
o Applications that use this media type: DNS
o Fragment identifier considerations: n/a
o Additional information:
Magic number(s): n/a File extension(s): n/a Macintosh file type
code(s): n/a
o Person & email address to contact for further information:
Tirumaleswar Reddy, kondtir@gmail.com
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Tirumaleswar Reddy, kondtir@gmail.com
o Change Controller: IESG
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o Provisional registration? No
11.2. JSON Web Token Claims Registration
11.2.1. Registry Contents Additions Requested
IANA is requested to assign the following claims in the registry
maintained in: https://www.iana.org/assignments/jwt/jwt.xhtml.
o Claim Name: 'server'
o Claim Description: DNS server identity
o Change Controller: IESG
o Specification Document(s): Section 5.2.1 of [THIS_DOCUMENT]
o Claim Name: 'policyinfo'
o Claim Description: Policy information of DNS server.
o Change Controller: IESG
o Specification Document(s): Section 5.2.2 of [THIS_DOCUMENT]
11.3. DNS Resolver Information Registration
IANA will add the names "attested-resinfo", "server", "filtering",
"resinfourl", "extendeddnserror" and "qnameminimization" to the SVCB
Service Parameters registry defined in Section 14.3 of
[I-D.ietf-dnsop-svcb-https].
IANA will add "malwareblocking", "phishingblocking",
"policyblocking", "filteredblocking" and "censoredblocking" sub-
attributes contained in the "filtering" attribute to the SVCB Service
Parameters registry.
IANA will add "adn" and "uri" sub-attributes contained in the
"server" attribute to the SVCB Service Parameters registry.
12. Acknowledgments
This specification leverages some of the work that has been done in
[RFC8225]. Thanks to Tommy Jensen, Ted Lemon, Paul Wouters, Neil
Cook, Vittorio Bertola, Vinny Parla, Chris Box, and Shashank Jain for
the discussion and comments.
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13. References
13.1. Normative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <https://www.rfc-editor.org/info/rfc6979>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
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[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <https://www.rfc-editor.org/info/rfc7638>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
13.2. Informative References
[I-D.btw-add-home]
Boucadair, M., Reddy.K, T., Wing, D., Cook, N., and T.
Jensen, "DHCP and Router Advertisement Options for
Encrypted DNS Discovery", draft-btw-add-home-12 (work in
progress), January 2021.
[I-D.btw-add-ipsecme-ike]
Boucadair, M., Reddy.K, T., Wing, D., and V. Smyslov,
"Internet Key Exchange Protocol Version 2 (IKEv2)
Configuration for Encrypted DNS", draft-btw-add-ipsecme-
ike-01 (work in progress), September 2020.
[I-D.ietf-dnsop-svcb-https]
Schwartz, B., Bishop, M., and E. Nygren, "Service binding
and parameter specification via the DNS (DNS SVCB and
HTTPS RRs)", draft-ietf-dnsop-svcb-https-02 (work in
progress), November 2020.
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[I-D.ietf-dnsop-terminology-ter]
Hoffman, P., "Terminology for DNS Transports and
Location", draft-ietf-dnsop-terminology-ter-02 (work in
progress), August 2020.
[I-D.ietf-dprive-dnsoquic]
Huitema, C., Mankin, A., and S. Dickinson, "Specification
of DNS over Dedicated QUIC Connections", draft-ietf-
dprive-dnsoquic-01 (work in progress), October 2020.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-08 (work in progress),
December 2020.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015,
<https://www.rfc-editor.org/info/rfc7626>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
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[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/info/rfc8914>.
[UNICODE] The Unicode Consortium, "The Unicode Standard", June 2016,
<http://www.unicode.org/versions/latest/>.
Appendix A. Example of ES256-based PAT JWS Serialization and Signature
For PAT, there will always be a JWS with the following members:
o 'protected', with the value BASE64URL(UTF8(JWS Protected Header))
o 'payload', with the value BASE64URL (JWS Payload)
o 'signature', with the value BASE64URL(JWS Signature)
This example will follow the steps in JWS [RFC7515] Section 5.1,
steps 1-6 and 8 and incorporates the additional serialization steps
required for PAT.
Step 1 for JWS references the JWS Payload, an example PAT Payload is
as follows:
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"filtering": {
"malwareblocking": true,
"policyblocking": false
},
"qnameminimization":false
}
}
This would be serialized to the form (with line break used for
display purposes only):
{"exp":1443640345,"iat":1443208345,"policyinfo":{
"filtering":{"malwareblocking": true,"policyblocking": false},
"qnameminimization":false},"server":{"adn":["example.com"]}}
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Step 2 Computes the BASE64URL(JWS Payload) producing this value (with
line break used for display purposes only):
eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6e
yJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9ja2
luZyI6ZmFsc2V9LCJxbmFtZW1pbmltaXphdGlvbiI6ZmFsc2V9LCJzZXJ2ZXIiOns
iYWRuIjpbImV4YW1wbGUuY29tIl19fQ
For Step 3, an example PAT Protected Header comprising the JOSE
Header is as follows:
{
"alg":"ES256",
"typ":"pat",
"x5u":"https://cert.example.com/pat.cer"
}
This would be serialized to the form (with line break used for
display purposes only):
{"alg":"ES256","typ":"pat","x5u":"https://cert.example.com
/pat.cer"}
Step 4 Performs the BASE64URL(UTF8(JWS Protected Header)) operation
and encoding produces this value (with line break used for display
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
eGFtcGxlLmNvbS9wYXQuY2VyIn0
Step 5 and Step 6 performs the computation of the digital signature
of the PAT Signing Input ASCII(BASE64URL(UTF8(JWS Protected
Header)) || '.' || BASE64URL(JWS Payload)) using ES256 as the
algorithm and the BASE64URL(JWS Signature).
TF_FZ_44WqL9nYiik8QBm-e1S-lJTOkRpaKLNc5SwnU86lbeccxhd2Xd3xd13cTj
ub65Pz1vhEQN1nzbZb2Hkg
Step 8 describes how to create the final PAT token, concatenating the
values in the order Header.Payload.Signature with period ('.')
characters. For the above example values this would produce the
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following (with line breaks between period used for readability
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
eGFtcGxlLmNvbS9wYXQuY2VyIn0
.
eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6e
yJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9ja2
luZyI6ZmFsc2V9LCJxbmFtZW1pbmltaXphdGlvbiI6ZmFsc2V9LCJzZXJ2ZXIiOns
iYWRuIjpbImV4YW1wbGUuY29tIl19fQ
.
TF_FZ_44WqL9nYiik8QBm-e1S-lJTOkRpaKLNc5SwnU86lbeccxhd2Xd3xd13cTjub
65Pz1vhEQN1nzbZb2Hkg
A.1. X.509 Private Key in PKCS#8 Format for ES256 Example**
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgevZzL1gdAFr88hb2
OF/2NxApJCzGCEDdfSp6VQO30hyhRANCAAQRWz+jn65BtOMvdyHKcvjBeBSDZH2r
1RTwjmYSi9R/zpBnuQ4EiMnCqfMPWiZqB4QdbAd0E7oH50VpuZ1P087G
-----END PRIVATE KEY-----
A.2. X.509 Public Key for ES256 Example**
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEVs/o5+uQbTjL3chynL4wXgUg2R9
q9UU8I5mEovUf86QZ7kOBIjJwqnzD1omageEHWwHdBO6B+dFabmdT9POxg==
-----END PUBLIC KEY-----
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures
The JWS payload used in this example as follows.
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"filtering": {
"malwareblocking": true,
"policyblocking": false
},
"qnameminimization":false
}
}
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This would be serialized to the form (with line break used for
display purposes only):
{"exp":1443640345,"iat":1443208345,"policyinfo":{
"filtering":{"malwareblocking": true,"policyblocking": false},
"qnameminimization":false},"server":{"adn":["example.com"]}}
The JWS protected Header value used for the first signature is same
as that used in the example in Appendix A. The X.509 private key
used for generating the first signature is same as that used in the
example in Appendix A.1.
The JWS Protected Header value used for the second signature is:
{
"alg":"ES384",
"typ":"pat",
"x5u":"https://cert.audit-example.com/pat.cer"
}
The complete JWS JSON Serialization for these values is as follows
(with line breaks within values for display purposes only):
{
"payload":
"eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6
eyJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9j
a2luZyI6ZmFsc2V9LCJwcml2YWN5dXJsIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9j
b21taXRtZW50LXRvLXByaXZhY3kvIiwicW5hbWVtaW5pbWl6YXRpb24iOmZhbHNl
fSwic2VydmVyIjp7ImFkbiI6WyJleGFtcGxlLmNvbSJdfX0",
"signatures":[
{"protected":"eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
zOi8vY2VydC5leGFtcGxlLmNvbS9wYXQuY2VyIn0",
"signature": "4vQEAF_Vlp1Tr6sJmS4pnIKDRmIjH8EZzY5BMT2qJCHD8PmjBk
tWVnlmbmyHs05GKauRBdIFnfp3oDPbE0Jq4w"},
{"protected":"eyJhbGciOiJFUzM4NCIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
zOi8vY2VydC5hdWRpdC1leGFtcGxlLmNvbS9wYXQuY2VyIn0",
"signature":dcvLlWp5q5sHcqRvAvVNrctGhbaV0TWPXeuwXDpcKSnkeT2eg1_5
D_4aozCFBYHkaxRPj06BliFwDnFMapjWBLbMDYLxr5O_LuSWLE1w8NkEHacWuHlA
90gKR8jd5hNX"}]
}
B.1. X.509 Private Key in PKCS#8 format for E384 Example**
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-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgevZzL1gdAFr88hb2
OF/2NxApJCzGCEDdfSp6VQO30hyhRANCAAQRWz+jn65BtOMvdyHKcvjBeBSDZH2r
1RTwjmYSi9R/zpBnuQ4EiMnCqfMPWiZqB4QdbAd0E7oH50VpuZ1P087G
-----END PRIVATE KEY-----
B.2. X.509 Public Key for ES384 Example**
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEVs/o5+uQbTjL3chynL4wXgUg2R9
q9UU8I5mEovUf86QZ7kOBIjJwqnzD1omageEHWwHdBO6B+dFabmdT9POxg==
-----END PUBLIC KEY-----
Authors' Addresses
Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
Dan Wing
Citrix Systems, Inc.
USA
Email: dwing-ietf@fuggles.com
Michael C. Richardson
Sandelman Software Works
USA
Email: mcr+ietf@sandelman.ca
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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